Two female child detainees sleep in a holding cell last month in Nogales, Ariz. An influx of Central American children reached 20,805 in fiscal 2013 and 39,133 between last October and June 15.

Voter ID laws are back in the news this week after a group of college students joined a lawsuit challenging North Carolina's new restrictive rules. And it's not just ID laws — Republican state legislatures have been busy devising all manner of creative ways to make voting more difficult for traditionally Democratic-leaning groups.

Related News/Archive

All of these restrictive measures take their justification from a perceived need to prevent "voter fraud." But there is overwhelming scholarly and legal consensus that voter fraud is vanishingly rare, and in fact nonexistent at the levels imagined by voter ID proponents. That hasn't stopped many Republican lawmakers from crying "fraud" every time they're faced with an unfavorable election outcome.

For reference, a roundup of the latest research is below. (Google each title to read the original report.)

Academic research

"The Truth About Voter Fraud," by Justin Levitt of Loyola Law School. Levitt performed a wide-ranging analysis of alleged incidents of voter fraud across the United States. "Usually, only a tiny portion of the claimed illegality is substantiated — and most of the remainder is either nothing more than speculation or has been conclusively debunked."

"The Politics of Voter Fraud," by Lorraine Minnite of Columbia University. Minnite concludes that voter fraud is exceedingly rare, and that the few allegations in the record usually turn out to be something other than voter fraud: "A review of news stories over a recent two-year period found that reports of voter fraud were most often limited to local races and individual acts and fell into three categories: unsubstantiated or false claims by the loser of a close race, mischief and administrative or voter error."

"Fraudulent Votes, Voter Identification and the 2012 U.S. General Election," by John Ahlquist and Kenneth R. Mayer of the University of Wisconsin, and Simon Jackman of Stanford. The authors conducted a survey experiment "to measure the prevalence of two specific types of voter fraud: repeat/fraudulent ballot casting and vote buying." Their conclusion: "The notion that voter impersonation is a widespread behavior is totally contradicted by these data."

"Voter Identifications Laws," by Minnite again. "In 95 percent of so-called 'cemetery voting' alleged in the 2010 midterm election in South Carolina, human error accounts for nearly all of what the state's highest law enforcement official had informed the U.S. Department of Justice was fraud."

"Caught in the Act: Recent Federal Election Fraud Cases," by Delia Bailey of the Washington University in St. Louis. Bailey unearthed only nine federal election fraud cases occurring between 2000 and 2005.

"They Just Do Not Vote Like They Used To: A Methodology to Empirically Assess Election Fraud," by M.V. Hood III of the University of Georgia and William Gillespie of Kennesaw State University. "After examining approximately 2.1 million votes cast during the 2006 general election in Georgia, we find no evidence that election fraud was committed under the auspices of deceased registrants."

"Identifying Election Fraud Using Orphan and Low Propensity Voters," by Ray Christensen and Thomas Schulz of Brigham Young University. The authors devise a new test for identifying instances of voter fraud; turn up no new instances of voter fraud.

Government investigations

A two-year investigation by Iowa's Republican secretary of state found evidence of 117 possible fraudulent votes and led to just six — six! — criminal convictions. In 2011 a Wisconsin task force found enough evidence to charge 20 people with fraudulent voting in the 2008 elections. Most of these were felons who were ineligible to vote. Kansas' secretary of state examined 84 million votes cast in 22 states to look for duplicate registrants. In the end 14 cases were referred for prosecution, representing 0.00000017 percent of the votes cast. A 10-year "death audit" in North Carolina turned up a grand total of 50 instances in which a vote may have been attributed to a deceased person, most likely due to errors made by precinct workers.

Court rulings

In striking down Wisconsin's voter ID law this spring, district judge Lynn Adelman wrote, "The evidence at trial established that virtually no voter impersonation occurs in Wisconsin. The defendants could not point to a single instance of known voter impersonation occurring in Wisconsin at any time in the recent past."

Christopher Ingraham is a data journalist focusing primarily on issues of politics, policy and economics. He previously worked at the Brookings Institution and the Pew Research Center.